A reluctance motor is a motor that generates torque using a configuration in which slit-shaped flux barriers are formed in a rotor core such that a magnetic resistance difference is generated in a rotation direction of a rotor. This type of reluctance motor is advantaged over an inductance motor (induction machine) in that secondary copper loss does not occur in the rotor and so on. In the light of these advantages, reluctance motors are gaining attention as motors used in applications such as air-conditioners and automobiles.
However, a reluctance motor typically generates a large torque ripple, and therefore further improvements are required to enable a reluctance motor to be used in the above applications.
As noted above, the principle by which a reluctance motor generates output torque is the magnetic resistance difference generated in the rotation direction of the rotor. This output torque is known as reluctance torque T, and is expressed by a following equation.T=Pn(Ld−Lq)id×iq 
Here, Pn denotes the number of pole pairs, Ld denotes d axis inductance, Lq denotes q axis inductance, id denotes a d axis current, and iq denotes a q axis current. It is evident from the above equation that in order to achieve an improvement in efficiency by increasing the torque generated in accordance with the current of the reluctance motor, it is effective to increase Ld−Lq, i.e. the difference between the d axis inductance and the q axis inductance.
It is also known that in order to increase a power factor, Ld/Lq, i.e. the ratio of the d axis inductance to the q axis inductance, should be increased. The value of the ratio Ld/Lq is typically referred to as a salient pole ratio.
To increase the difference Ld−Lq and the salient pole ratio Ld/Lq, a plurality of layers of slits known as flux barriers are provided in a rotor core of the reluctance motor. In so doing, d axis magnetic paths facilitating the flow of magnetic flux are formed in directions corresponding to the plurality of layers of slits, and magnetic resistance on q axis magnetic paths crossing the plurality of layers of slits is increased.
The following configuration is an example of prior art employed to reduce the torque ripple using the flux barrier structure described above as a basic structure (see PTL 1, for example).
As a rotor laminated core for a reluctance motor disclosed in PTL 1, a plurality of arc-shaped slits projecting on a rotary shaft hole side are formed concentrically, and core pieces formed by arranging the plurality of arc-shaped slits at intervals around the rotary shaft hole are laminated.
In the rotor laminated core for a reluctance motor, which is rotated by reluctance torque generated on the basis of a difference in inductance between a salient pole direction, in which magnetic flux flows easily in an extension direction of the arc-shaped slits, and a non-salient pole direction, in which magnetic flux does not flow easily in a parallel direction to the extension direction of the arc-shaped slits, end portions of the plurality of arc-shaped slits are formed at equal intervals around the entire circumference of the core piece. By employing this configuration, PTL 1 achieves a reduction in the torque variation, or in other words the torque ripple, of the rotor.